This invention relates in general to optical devices and, more particularly, to optical devices which use a dispersive element to separate or combine optical signals.
A known technique for transmitting multiple signal components as a single optical signal is known as wavelength division multiplexing (WDM). In a WDM signal, each signal component has a respective different frequency or wavelength. Each frequency or wavelength is sometimes referred to as a channel. Various devices have been developed to optically separate or combine the signal components, including multiplexers, demultiplexers and optical add/drop modules. There is a progressively growing demand in the market for devices of this type which have a high channel count, or in other words which can handle optical signals with a large number of signal components at respective different frequencies. Currently, there is a growing demand for devices capable of handling optical signals with 16 to 80 signal components, or an even greater number of signal components. There is also a demand for these devices to have a low insertion loss, and to be packaged in a compact manner.
In attempt to meet this demand, devices have been developed which utilize a dispersive element to facilitate optical separation or combination of multiple signal components. In order to reliably achieve satisfactory performance, these devices are manufactured according to extremely tight tolerances for a number of different physical and optical characteristics. An example of one such device is a demultiplexer which has the end of an input fiber and the ends of several output fibers secured at predetermined locations on a support member, and which has optical and dispersive components disposed on the support member between the input and output fibers so that each signal component of a WDM signal arriving through the input fiber is focused on the end of a respective output fiber. In this device, the support member and the optical and dispersive components are all fabricated according to extremely strict tolerences to ensure that, when the device is put into production, each signal component will be fairly accurately focused onto the end of a respective output fiber in each production device.
While pre-existing devices of this type have been generally adequate for their intended purposes, they have not been satisfactory in all respects. For example, the need for extremely tight tolerances as to a large number of physical and optical characteristics causes these devices to have a number of components which are each very expensive to manufacture. As a result, the device itself is undesirably expensive. Moreover, despite the use of tight tolerances, not every signal component ends up being accurately focused on the end of the corresponding output fiber. Consequently, characteristics like insertion loss are not always optimum, and may vary from system to system, for example where a given subset of tolerance variations offset each other in one system, but are cumulative in another system.
From the foregoing, it may be appreciated that a need has arisen for a method and apparatus that will avoid at least some of the disadvantages involved in pre-existing approaches. One form of the invention encompasses a method which involves: fixedly supporting on a support section a further section which is operable to transport radiation containing a plurality of signal components at respective different frequencies along a path of travel; fixedly supporting a dispersive section on the support section so that the signal components pass therethrough, the dispersive section having a dispersive characteristic that deviates a direction of travel of each signal component by a respective different amount so as to effect an optical mapping for each signal component between the path of travel associated with the further section and a respective further path of travel; providing a plurality of optical fibers which each correspond to a respective signal component; positioning an end of each optical fiber in the region of a respective further path of travel; for each optical fiber, causing a beam of radiation which includes the corresponding signal component to travel along one of a path of travel through that optical fiber and the path of travel associated with the further section, and to then be optically mapped by the dispersive section to the other thereof; and adjusting a position of the end of each fiber while monitoring the amount of the corresponding signal component traveling along the other of the paths of travel, until the end of that fiber is disposed in a selected position, and then fixing the end of that fiber in the selected position thereof with respect to the support section.
A different form of the invention encompasses an apparatus which involves: a first portion which includes a support section and a further section fixedly supported on the support section, the further section being operable to transport radiation containing a plurality of signal components at respective different frequencies along a path of travel; a second portion which includes a dispersive section fixedly supported on the support section so that the signal components pass therethrough, and having a dispersive characteristic that deviates a direction of travel of each signal component by a respective different amount so as to effect an optical mapping for each signal component between the path of travel associated with the further section and a respective further path of travel; a third portion which includes a plurality of optical fibers that each correspond to a respective signal component, and that each have an end which is initially positioned in the region of a respective further path of travel; a fourth portion which, for each optical fiber, is operable to cause a beam of radiation which includes the corresponding signal component to travel along one of a path of travel through that optical fiber and the path of travel associated with the further section, and to then be optically mapped by the dispersive section to the other thereof; and a fifth portion which is operable to adjust a position of the end of each fiber while monitoring the amount of the corresponding signal component traveling along the other of the paths of travel, until the end of that fiber is disposed in a selected position, and to then fix the end of that fiber in the selected position thereof with respect to the support section.
Still another form of the invention encompasses an apparatus which involves: a support section; a further section supported on the support section and operable to transport radiation containing a plurality of signal components at respective different frequencies along a path of travel; an optically transmissive substrate fixedly supported on the support section, the substrate having a surface on one side thereof; a plurality of optical fibers that each have an end portion which is fixedly coupled to the substrate with an end thereof adjacent the surface on the substrate, each optical fiber being operable to carry a respective signal component;
and a dispersive section fixedly supported on the support section at a location disposed optically between the further section and the substrate so that the signal components pass therethrough, and having a dispersive characteristic that deviates a direction of travel of each signal component by a respective different amount so as to effect an optical mapping for each signal component between the end portion of a respective optical fiber and the path of travel associated with the further section.